Adult: Aorta
Reappraisal of the role of motor and somatosensory evoked potentials during open distal aortic repair

Read at the 100th Annual Meeting of The American Association for Thoracic Surgery: A Virtual Learning Experience, May 22-23, 2020.
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Abstract

Objective

Intraoperative motor and somatosensory evoked potentials have been applied to monitor spinal cord ischemia during repair. However, their predictive values remain controversial. The purpose of this study was to evaluate the impact of motor evoked potentials and somatosensory evoked potentials on spinal cord ischemia during open distal aortic repair.

Methods

Our group began routine use of both somatosensory evoked potentials and motor evoked potentials at the end of 2004. This study used a historical cohort design, using risk factor and outcome data from our department's prospective registry. Univariate and multivariable statistics for risk-adjusted effects of motor evoked potentials and somatosensory evoked potentials on neurologic outcome and model discrimination were assessed with receiver operating characteristic curves.

Results

Both somatosensory evoked potentials and motor evoked potentials were measured in 822 patients undergoing open distal aortic repair between December 2004 and December 2019. Both motor evoked potentials and somatosensory evoked potentials were intact for the duration of surgery in 348 patients (42%). Isolated motor evoked potential loss was observed in 283 patients (34%), isolated somatosensory evoked potential loss was observed in 18 patients (3%), and both motor evoked potential and somatosensory evoked potential loss were observed in 173 patients (21%). No spinal cord ischemia occurred in the 18 cases with isolated somatosensory evoked potential loss. When both signals were lost, signal loss happened in the order of motor evoked potentials and then somatosensory evoked potentials. Immediate spinal cord ischemia occurred in none of those without signal loss, 4 of 283 (1%) with isolated motor evoked potential loss, and 15 of 173 (9%) with motor evoked potential plus somatosensory evoked potential loss. Delayed spinal cord ischemia occurred in 12 of 348 patients (3%) with intact evoked potentials, 24 of 283 patients (8%) with isolated motor evoked potentials loss, and 27 of 173 patients (15%) with motor evoked potentials + somatosensory evoked potentials loss (P < .001). Motor evoked potentials and somatosensory evoked potentials loss were each independently associated with spinal cord ischemia. For immediate spinal cord ischemia, no return of motor evoked potential signals at the conclusion of the surgery had the highest odds ratio of 15.87, with a receiver operating characteristic area under the curve of 0.936, whereas motor evoked potential loss had the highest odds ratio of 3.72 with an area under the curve of 0.638 for delayed spinal cord ischemia.

Conclusions

Somatosensory evoked potentials and motor evoked potentials are both important monitoring measures to predict and prevent spinal cord ischemia during and after open distal aortic repairs. Intraoperative motor evoked potential loss is a risk for immediate and delayed spinal cord ischemia after open distal aortic repair, and somatosensory evoked potential loss further adds predictive value to the motor evoked potential.

Graphical abstract

Impact of intraoperative MEP and SSEP loss on SCI during open distal aortic repair is demonstrated.

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Section snippets

Materials and Methods

The Committee for Protection of Human Subjects, the local Institutional Review Board, approved this study. This study used a historical cohort design, using risk factor and outcome data from our department's prospective registry. Patients who underwent open distal aortic repair (descending thoracic and TAAA) with both MEP and SSEP monitoring during December 2004 and December 2019 were included in the study. Indications for surgical interventions included symptomatic aneurysm, aneurysm size

Results

Of 930 open distal aortic repairs performed during the study period, both SSEP and MEP were recorded on 822 patients. Of 822 SSEP measurements, 202 were missing popliteal fossa measurements. Both MEP and SSEP were intact for the duration of surgery in 348 patients (42%). A total of 283 patients (34%) had isolated MEP loss, 18 patients (3%) had isolated SSEP loss, and 173 patients (21%) had both MEP and SSEP loss. Preoperative patient characteristics are summarized in Table 1, and intraoperative

Discussion

Our data showed that isolated MEP loss and the combination of MEP and SSEP loss were predictive of immediate and delayed-onset SCIs (Figure 6). It is not surprising that patients without return of lost signals—which indicate ongoing damages in the ventral and posterior spinal cord—had higher ORs for immediate SCI compared with patients who had only transient signal changes as normal MEP and SSEP at the conclusion of surgery. The predictabilities of immediate SCI with transient MEP and SSEP loss

Conclusions

SSEP and MEP are both important monitoring measures to predict and prevent SCI during distal aortic repairs (Video 1). When these signals were interrupted, and especially when both were affected, rates of immediate SCI were high—especially when those were not regained at the conclusion of the procedures. In addition, intraoperative MEP and SSEP loss were associated with delayed SCI.

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